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 Large number of different types of separator are now commercially available  Many are not of the traditional design and, as such, are not covered, by a standard  However, many of the new designs show promise and deserve further investigation Grease separator selection

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 The standard (EN 1825)  Difficult to understand (information spread between Part 1 and Part 2)  Only considers conventional ‘large’ underground separators – Not practical for most town centre catering outlets  No consideration of more recent separator designs, including skimmers. Grease separator standard

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Grease separator standard (2)  The standard (EN 1825)  Does not consider hybrids – Dosing and separators  Most separator suppliers don’t understand EN 1825 ● Suppliers have a variety of sizing methods ● Seems to be little standardisation but plenty of confusion ● Often, sizing is only for the food trap part of the separator

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Jetting and cleaning  The most frequent symptom of FOG in the sewer system is a blockage  Sewer blockages may occur at any point on the sewer system, from the point of source to the wastewater treatment works  Sewer blockages can be categorised as a primary or secondary blockage

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Jetting and cleaning  Primary FOG related blockages are due to natural deposition of FOG at a specific location as a result of the combination of:  a source and appropriate type of FOG,  concentration of FOG in the flow,  the natural processes of separation, and  hydraulic conditions

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Jetting and cleaning  Secondary FOG blockages are those that occur as a direct result of a previous blockage or severe flow restriction.  Flow velocity upstream of the original blockage will reduce - FOG that would otherwise remain in the flow will separate out.  FOG will be high on the pipe wall or in the crown of the upstream pipe, due to the increased depth of flow  Sewer debris, (sanitary towels and other sewage debris) then sticks to the FOG on the crown of small pipes, a secondary blockage subsequently develops

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Jetting and cleaning practice The following may seem obvious BUT experience often shows otherwise !  All FOG related blockages must be effectively cleared and the upstream pipe effectively cleaned to prevent repeat incidents  A recommended procedure has been proposed to ensure effective cleansing

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Jetting and cleaning practice (2)  General purpose jets are a compromise  Removal of FOG from a sewer should be carried out as a staged and incremental process 1. General purpose jet to remove soft debris 2. Plough to remove hard sediments, 3. Spinning jet to remove FOG 4. Survey with a camera

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Existing sewer improvements (3)  Where existing systems need to be altered to reduce CSO spills etc, ensure that the ‘improvement’ will not result in areas of low velocity/tranquil flow where serious FOG deposition could occur.  Similarly, where storage needs to be added to reduce sewer flooding (These may seem obvious, but they have happened)

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New sewer design to avoid FOG  The following should be done as good practice, to ensure there are no areas with very low velocity:  Pipe velocity, 0.6 m/s or greater  Use minimum number of pipe joints (joints dissipate energy in small flows)  Use easier to clean pipe materials  Good detailing of connections (saddles etc)  Good detailing in manholes

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Pumping station design  Greater likelihood of FOG build up with:  Higher concentration of FOG  Low velocity/movement in the wet well: ● More tranquil the effluent in the wet well ● If there are dead zones in the wet well